Field of the Invention
The present invention relates to a light emitting diode (LED) assembly, and more particularly, to an LED assembly having an excellent heat radiation structure and a liquid crystal display device including the LED assembly.
Discussion of the Related Art
Recently, as the information society progresses, display devices processing and displaying a large amount of information have rapidly advanced and various flat panel displays (FPDs) have been developed. Specifically, the FPDs such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, organic light emitting diode (OLED) display devices and field emission display (FED) devices, which have superior characteristics such as thin profile, light weight and low power consumption, have replaced cathode ray tubes (CRT).
Among various FPDs, LCD devices, which have various advantages of high contrast ratio, displaying moving images and low power consumption, have been used in various fields such as notebooks, monitors and televisions. LCD devices take advantage of the optical anisotropy and polarization properties of liquid crystal molecules.
An LCD device includes a liquid crystal panel having two substrates facing each other, with a liquid crystal layer between the two substrates, and obtains difference in transmittance by changing an alignment direction of the liquid crystal molecules with an electric field in the liquid crystal panel.
Since the LCD device is a non-emissive type display device, an additional light source is required for the LCD device. As a result, a backlight unit including a light source is disposed under the liquid crystal panel. For example, one of a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL) and a light emitting diode (LED) may be used as the light source of a backlight unit (e.g., unit 20 in FIG. 1). Among various light sources, the LED has been widely used as the light source for its various features such as a small size, a low power consumption and a high reliability.
FIG. 1 is a cross-sectional view showing a liquid crystal display (LCD) device using a light emitting diode (LED) as a light source according to the related art.
In FIG. 1, an LCD device includes a liquid crystal panel 10, a backlight unit 20, a main frame 30, a top frame 40 and a bottom frame 50.
The liquid crystal panel 10 displaying an image includes first and second substrates 12 and 14 facing and spaced apart from each other and a liquid crystal layer interposed therebetween. Polarizing plates 19a and 19b are disposed on outer surfaces of the first and second substrates 12 and 14, respectively.
The backlight unit 20 is disposed under the liquid crystal panel 10. The backlight unit 20 includes a light source of a light emitting diode (LED) assembly 29 disposed along at least one side of the main frame 30, a reflecting plate 25 of a white color or a silver color on the bottom frame 50, a light guide plate 23 on the reflecting plate 25, and an optical sheet 21 on the light guide plate 23.
The liquid crystal panel 10 and the backlight unit 20 are surrounded by the main frame 30 of a rectangular ring shape. The top frame 40 covering a top edge portion of the liquid crystal panel 10 and the bottom frame 50 covering a rear surface of the backlight unit 20 are combined with the main frame 30 to modularize the liquid crystal panel 10 and the backlight unit 20.
The LED assembly 29 includes an LED 29a and an LED printed circuit board (PCB) 29b having the LED 29a thereon. The LED assembly 29 is fixed such that a light emitted from the LED 29a enters an incident surface of the light guide plate 23. After the light from the LED 29a enters the light guide plate 23 through the incident surface, the light is refracted toward the liquid crystal panel 10. While passing through the optical sheet 21, the light refracted in the light guide plate 23 and the light reflected by the reflecting plate 25 are processed as a surface light source having a high uniformity and a high quality to be supplied to the liquid crystal panel 10.
A temperature of the LED 29a sharply increases according to the duration of usage and the increase in temperature causes a change in lifetime and luminance. Accordingly, when the LED 29a is used as a light source of the backlight unit 20, a design of heat radiation according to the increase in the temperature of the LED 29a is one of the most important considerations.
However, since the LCD device according to the related art does not have a structure for radiating a heat of high temperature generated by the LED 29a promptly, the temperature of the LED 29a gradually increases in operation. As a result, the change in luminance causes reduction in display quality.
In addition, the lifetime of the LED 29a is reduced by increase in temperature. Specifically, the LED 29a may be formed on a flexible printed circuit board (FPCB) of an epoxy group based on a light weight, a thin profile and a flexibility of the LCD device. Since the FPCB of an epoxy group has a relatively low heat transfer coefficient, problems due to the increase in the temperature of the LED 29a are exacerbated.